There was a long debate on the now defunct BBC food message board a while back - the jury was still out on whether supermarket meals could be beaten on cost by fresh.
The undeniable pros of cooking fresh from scratch can easily overlook the true cost if
everything is counted, meaning wastage like veg peelings; also cost of store cupboard items (oil, spices/sauces, cornflour/gravy powder etc) or fridge (typically eggs/milk) and also gas/elec and the water for washing up, petrol/fares. The cost of a meal isn't just the price of the meat or fish, as some TV chefs suggest having built a dish around it, no pudding of course.
Most people agreed that whilst home-baked cakes, crumbles and pies taste better, the cost is likely to be twice that of a supermarket, who can bulk-buy. Growing teenagers and active people need calories. Perhaps Jamie should be promoting a low GI diet instead, e.g.:
http://www.the-gi-diet.org/lowgifoods/
I know people on this board watched the BBC programme a month or so ago in which James Martin and Angela Hartnett tried to cook for people on limited budgets, going over, but did OK for feeding 100 (much easier than for 1 or 2) so the honoured guests were left with the impression that "it could be done" since the chefs obviously couldn't allow themselves to fail, so missing the whole point of the difficulty that the programme had shown throughout.
Eating from scratch IMO is expensive, so we'll see what Jamie achieves eh?